Technical Abstract:
A mixture experimental design, a variant of response surface methodology, was conducted to determine the proportion of time to feed broiler starter (23% protein), grower (20% protein) and finisher (18% protein) diets to optimize production and processing variables based on a total production time of 48 d. Mixture designs are useful for proportion problems where the components of the experiment (i.e., length of time the diets were fed) add up to a unity (48 d). The experiment was conducted with d old male Ross X Ross broiler chicks. The birds were placed 50 birds per pen in each of 60 pens. The experimental design was a 10 point augmented simplex-centroid design with six replicates of each point. Each design point represented the portion(s) of the 48 d that each of the diets was fed. Formulation of the diets was based on NRC standards. At 49 d, each pen of birds was evaluated for production data including BW, feed conversion, and cost of feed consumed. Then, six birds were randomly selected from each pen for processing data. Processing variables included live weight, hot carcass weight, dressing percent, fat pad percent, and breast yield (Pectoralis major and Pectoralis minor weights). Production and processing data were fit to simplex regression models. Model terms not determined to be significant (P<0.05) were removed. The models were found to be statistically adequate for analysis of the response surfaces. A compromise solution was calculated based on optimal constraints designated for the production and processing data. The results indicated that broilers fed a starter and finisher diet for 30 d and 18 d, respectively would meet the production and processing constraints. Trace plots showed that the production and processing variables were not very sensitive to the grower diet. The results of the mixture experiment concluded the grower diet was not needed for a 48 d production period.